1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for reporting measurement results in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
The 3GPP LTE-A employs various techniques such as carrier aggregation, relay, etc. The 3GPP LTE system is a single carrier system supporting only one bandwidth (i.e., one component carrier) among {1.4, 3, 5, 10, 15, 20} MHz. On the other hand, the LTE-A employs multiple carriers using carrier aggregation. The carrier is defined with a center frequency and a bandwidth. A multiple-carrier system uses a plurality of component carriers having a narrower bandwidth than a full bandwidth.
A user equipment (UE) persistently performs measurement to maintain quality of a radio link with a serving cell from which the UE receives a service. A cell or frequency to be measured is referred to as a measurement object, and is associated with a reporting configuration for independently triggering reporting of a measurement result for each measurement object. The UE performs measurement on the measurement objects, and when the reporting configuration is satisfied, reports the measurement result to a base station (BS).
According to the conventional measurement procedure, measurement is configured to the UE for each frequency. However, in the multiple-carrier system, a plurality of cells may be configured to the UE. When the plurality of cells use different frequencies, a plurality of measurement configurations are given to the UE, and then a measurement reporting time are differently configured for each measurement configuration. Since the network cannot concurrently receive measurement results for frequencies, the network cannot configure the plurality of cells to the UE.
In the multiple-carrier system, the number of cells configured to the UE is not fixed. Instead, the number of cells configured dynamically may vary. If the measurement configuration is modified whenever a new cell is added or a cell in use is deleted, signaling overhead may increase.